In the general practice of forming fibrous web materials, such as airformed webs of absorbent material, it has been common to utilize a fibrous sheet of cellulosic or other suitable absorbent material which has been fiberized in a conventional fiberizer, or other shredding or comminuting device, to form discrete fibers. In addition, particles of superabsorbent material have been mixed with the fibers. The fibers and superabsorbent particles have then been entrained in an air stream and directed to a porous, foraminous forming surface upon which the fibers and superabsorbent particles have been deposited to form an absorbent fibrous web.
The forming surfaces utilized in such systems have been constructed with a wire screen or fluted grid, and a pneumatic flow mechanism, such as provided by a vacuum suction system, has been employed to define a differential pressure zone on the forming surface and impose a pressure differential thereon. The pressure difference has typically provided an airflow through the openings or perforations in the screen or grid of the forming surface. The use of vacuum suction to draw the air-entrained fiber stream onto the forming surface, and pass the airflow through the forming surface has been employed in high-speed commercial operations.
The prior practice of forming airformed fibrous webs has also employed various mechanisms to produce gradations in basis weight along the fibrous webs. For example, the mechanisms have been employed to produce gradations of basis weight along a longitudinal direction of the formed web, i.e., in the direction of movement of the fibrous web through the forming process. Conventional mechanisms have also been employed for providing basis weight variations along a transverse, cross-direction of the formed web.
To form an airlaid, stabilized web, binder materials have been added to the web structure. Such binder materials have included adhesives, powders, netting, and binder fibers. The binder fibers have included one or more of the following types of fibers: homofilaments, heat-fusible fibers, bicomponent fibers, meltblown polyethylene fibers, meltblown polypropylene fibers, and the like.
Conventional systems for producing airlaid, stabilized fibrous webs have mixed the binder fibers with absorbent fibers, and then deposited the mixed fibers onto a porous forming surface by using a vacuum system to draw the fibers onto the forming surface. Such conventional systems, however, have been limited with regard to the lengths of the binder fibers that can be efficiently employed. In the operation of the conventional systems, the lengths of the binder fibers have typically been 6 mm or less. Attempts to use longer binder fibers have caused plugging of distribution screens, non-uniform distribution of fibers, fiber clumping, and other basis weight uniformity problems.
Conventional systems for producing stabilized airlaid webs have required the use of excessive amounts of energy. Where the binder fibers are heat-activated to provide the stabilized web structure, it has been necessary to subject the fibrous web to an excessively long heating time to adequately heat the binder fibers. For instance, typical heating times with through-air bonding systems are in the range of 7-8 seconds. Additionally, it has been necessary to subject the fibrous web to an excessively long cooling time, such as during roll storage in warehouses, to establish and preserve the desired stabilized structure prior to further processing operations. As a result, such conventional systems have been inadequate for manufacturing stabilized airlaid webs directly in-line on consumer product converting machines at high-speeds. A previously used approach has been to manufacture wide, multi-lane base webs off-line. The wide webs have been slit and subsequently converted into desired products on separate manufacturing machines.
Conventional systems for producing off-line stabilized airlaid webs have been configured to make fibrous webs that have straight side edges and substantially uniform basis weights. The stabilized airlaid webs have been cut after the stabilization operation to provide segments of web material having shaped side edges suitable for use in typical consumer products such as feminine care products, diapers, children's training pants, adult incontinent products, and the like. As a result, such conventional systems have been inadequate for making fibrous structures having varied, contoured shapes and contoured basis weights. Additionally, the cutting and shaping of the selected segments of the stabilized web material has wasted excessive amounts of the stabilized material, and has excessively complicated the manufacturing operations. In addition, conventional systems have resulted in excessive costs associated with the shipping, storage, and roll handling of the relatively low density materials.